1. Field of the Invention
The present invention relates to a pressure-sensitive copying paper, more particularly, to a pressure-sensitive copying paper having a microcapsule layer containing a novel fluoran compound as a color former.
2. Description of the Prior Art
Pressure-sensitive copying papers generally comprise a transfer sheet having thereon a layer of fine capsules containing a solution of an electron donating colorless organic compound (hereinafter referred to as a "color former") in an organic solvent, and a receiving sheet having thereon a layer of an electron accepting solid. A suitable binder is generally used for coating the electron accepting solid.
When both sheets are put together in such a manner that the electron donating layer is brought into contact with the electron accepting layer and localized pressure is applied to the combination of sheets by handwriting or typewriting, the capsules are ruptured and the colorless color former contained in the capsules is adsorbed by the electron accepting solid, which is usually a solid acid, to form a color.
Pressure-sensitive copying paper systems comprising the aforesaid transfer sheet (hereinafter referred to as an "upper sheet") and a receiving sheet (hereinafter referred to as a "lower sheet") and an intermediate sheet (hereinafter referred to as a "middle sheet") are also known. In these systems, the middle sheet is usually coated, on opposite surfaces, with a layer of microcapsules containing a color former solution and with a layer of a solid acid and a binder, respectively.
Another type of pressure-sensitive copying system is a recording sheet which can be prepared by applying the above described microcapsules and the adsorbent solid acid on the same surface of a support.
The solid acid used in conventional types of pressure-sensitive copying papers includes active clay substances such as acid clay, attapulgite, zeolite, bentonite and the like, solid organic acids such as succinic acid, tannic acid, benzoic acid and the like, and acidic organic polymers such as phenol-formaldehyde polycondensates, phenol-acetylene copolymers, styrene-maleic anhydride copolymers containing residual acidic radicals, salicylic acid-formaldehyde polycondensates and the like.
The organic solvent for dissolving the color former which is conventionally used includes, for example, ethylene glycol, chlorobenzene, chlorodiphenyl, diethyl phthalate, trioctyl phosphate and alkylnaphthalene.